The cell membrane is semi-permeable, allowing smaller molecules to pass through via passive transport like diffusion and osmosis. Diffusion is the movement of particles from high to low concentration without energy, while osmosis is the diffusion of water through the semi-permeable membrane. In a hypotonic environment with a lower solute concentration outside the cell, osmosis causes water to enter the cell, potentially bursting it. In a hypertonic environment with a higher external solute concentration, osmosis causes water to exit the cell, potentially causing it to shrivel. An isotonic environment has equal internal and external solute concentrations, allowing the cell to remain stable.

2. Semi-Permeable
Membrane
 The cell membrane
is semi-permeable
 Semi-permeable-
only certain things
can pass through
(permeate) it
 Smaller molecules
can pass through.
 Larger molecules
and charged
molecules cannot.

3. Passive vs. Active Transport
 PASSIVE= **No energy (ATP) needed for
movement of certain particles across the
membrane in/out of cell.
 Particles (molecules and ions) move from
HIGH to LOW concentration.
 “Paddling with the current.”
 Types of passive transport
Diffusion
Osmosis

4. Diffusion
 Move from high to low
concentration
 Occurs until equilibrium is
reached.
 PASSIVE TRANSPORT, SO NO
ENERGY REQUIRED FOR
PARTICLES TO DIFFUSE!!!

5. Osmosis
 Osmosis-diffusion
of water
 PASSIVE, SO NO
ENERGY
REQUIRED TO DO
THIS!
 Water can go
through the semi-
permeable cell
membrane.
 High  low

6. Hypertonic Environments
 Osmosis can occur with water
going into OR out of the cell,
depending on what type of
environment the cell is in.
 Hyper= above/higher
 Hypertonic- the cell is in a higher
solute concentration
 i.e. saltwater
 Osmosis- water moves OUT
of cell in this environment
(highlow).
 Shrivel and die.

8. Plasmolysis
 Occurs when plant cells lose
water in hypertonic environment.

9. Hypotonic Environments
 Hypo = under/lower
 Hypotonic- the cell is in a
lower solute concentration
 i.e. pure water
 Osmosis- water will move
INTO cell in this
environment (highlow)
 Swells with water and bursts.

11. Osmotic Pressure
 The pressure that builds up inside a cell
due to a hypotonic environment (i.e. pure
water.)
 If pressure is too high, what happens?
 Osmotic pressure in plants = turgor
pressure.
 Cell wall prevents plant cells from bursting
—like a water balloon in a box

12. Isotonic Environments
 Iso = same/equal
 Isotonic cell environment-
equal solute concentration
inside and outside the cell
 i.e. pure blood
 Water flow in = water flow out
 Cells remain the same

13. 98% Water, 2% Salt 98% Water, 2% Salt
98% Water, 2% Salt
96% Water, 4% salt 100% Water, 0% Salt 98% Water, 2% Salt
Concentrated Saltwater Pure Water Blood